Chicago Green Alleys — Permeable-Pavement Alley Reconstruction, ~400 Built and Unevenly Sited

Chicago has roughly 1,900–2,000 miles of public alleys. After four pilot reconstructions funded from 2001, the city created a Green Alleys programme in 2006 and published a Green Alley Handbook in 2010, using permeable pavements, high-albedo surfaces and recycled materials to reduce basement flooding and sewer load.
Scale and cost: about 400 green alleys had been built by 2024, at roughly USD 250,000–500,000 per block. Construction ran at about 24 per year in 2007–2020 and about 30 per year in 2021–2023.
Performance: the city estimates a green alley design can return up to 80% of rainfall to the ground; this is a design estimate rather than a published programme-wide monitoring result.
Caveats: reporting by Block Club Chicago (2024) found that fewer than a third of alleys are on the South and West Sides, and nine of the ten wards with most alleys are in the North/Northwest, while South/West wards filed three of five flood-related 311 complaints citywide in 2021–2023. Funding comes largely from the $1.5 million annual aldermanic menu allocation, yielding 2–3 alleys per ward at most; an alderperson called siting 'a shot-in-the-dark implementation strategy'.

Read the full analysis: https://www.chicago.gov/city/en/depts/cdot/provdrs/street/svcs/green_alleys.html